1. Field of the Invention
The invention concerns method and apparatus for the detection of short circuits in electrical installations, in particular on railway contact wires, whereby a signal corresponding to the derivative with respect to time of the monitored current is generated and compared with at least one limit value. If the signal exceeds a limit value, a short circuit is indicated.
2. Description of the Prior Art
Monitoring devices of the kind stated are known whereby a signal proportional to the monitored current is itself monitored as to whether it exceeds a permissible limit value. Devices of this kind do not function correctly under operating conditions because service currents which are still acceptable are of the same order of magnitude as short-circuit currents. This is especially the case with the contact wires of electric railways, in particular direct-current systems, when several consumers (traction vehicles) impose a high and multiple load on a section of line between two power supply substations which are monitored with respect to the supply current. Under such circumstances, it is in general not the magnitude of the short-circuit currents which must be avoided, but the damage and risk of fire caused by the short circuits.